While not limited thereto, the present invention is particularly adapted for use in measuring the amount of scrubber carryover moisture appearing as a spray of dispersed water droplets. Such scrubbers are used, for example, to remove pollutants from the flue gases of coal-fired power plants. In the scrubber, the flue gases entrain liquor (i.e., water) droplets; and this water must be vaporized before the flue gases pass to the atmosphere. The amount of carryover moisture seriously affects the efficiency of a coal-fired power plant since, in order to vaporize the water droplets entrained in the flue gases, they must pass through steam coils or other heating apparatus which can use up to 5% of the total heat generated by the power plant. Accordingly, it is preferable to use some means for monitoring the carryover moisture level in order that the operating parameters of the scrubber can be optimized to minimize the water content of the scrubbed gas.
In the past, attempts have been made to measure carryover moisture with the use of see-through opacity devices such as smoke detectors and back-scattered laser beam single particle detectors. These devices, however, have met with only limited success. Each requires a stream of purging gas to keep the optical components clean, but the purging gas disturbs the environment in which measurements are taken, usually causing a low indication of particle mass. Additionally, high particle density can saturate the light detector primarily because of the fact that a very small finite field-of-view is employed in an attempt to isolate a single water droplet in the environment.